Endodontic treatment often saves a tooth from imminent extraction, but does not alone restore the tooth to its role as a long-term functioning member of the mouth. For example, endodontically treated teeth are more prone to fracture than vital teeth, perhaps because loss of nerve and vascular supply leads to loss of internal moisture and commensurate reduction in resilience of tooth structure. Furthermore, if caries has caused the death of the pulp of the tooth, eventuating the need for endodontic treatment, carious lesions in the tooth structure may cause the tooth to split under masticatory loads.
Certain well-known products and methods are available for use in the restoration of endodontically treated teeth. Cementing a metal post within the canal of an endodontically treated tooth is a common clinical procedure. If some or all of the coronal structure of the tooth has been compromised or lost, the post is fitted with a core to replace lost tooth structure. The combined post and core, sometimes referred to as a dowel and core or a dowel-core, is often fabricated of stainless steel or titanium or gold alloys. Typically, the restoration is completed with a crown.
Clinical considerations and methods with respect to metal posts and cores, and exemplary prefabricated posts, are generally discussed in Pastrana, Miguel A., D.M.D., "Restoration of Endodontically Treated Teeth", in Thayer, Keith E., ed., Fixed Prosthodontics, Year Bk. Med., 600 p., January, 1984. Pastrana discloses, for example, that endodontic treatment should be carefully preplanned so that the material from the filled tooth canal can be easily and adequately eliminated, the material of choice being gutta-percha. At the time of restoration, the entire diameter of gutta-percha is removed from the canal either to at least two-thirds of the root's length or to a depth equal to the length of the tooth's normal clinical crown. A pattern for the post and core is then made of wax or polymer resin, formed and built in the mouth, with the completed pattern then being sprued, invested and cast. Alternatively, prefabricated systems are available in which a prefabricated core is cemented in place with subsequent building up of the core with amalgam or composite resin.
Another publication in which metal post/core structures and the use thereof are discussed include Shillingberg, Herbert, et al., "Restoration of Endodontically Treated Teeth", in Shillingberg, Herbert, et al., Fundamentals of Fixed Prosthodontics, Quint Pub. Co., 339 p., 1978. Metal structures are discussed throughout.
Despite its many advantages, the post-and-core, or dowel-core, of an anterior restoration routinely presents subtle yet invidious cosmetic aberrations. Even with the most natural-looking crown atop the restoration, the restored tooth inevitably has an unmistakable "false" look attributable to its adjacent grayish or darkened gingiva. For example, as Geller et al. disclose in "The Willi's Glas Crown A New Solution in the Dark and Shadowed Zones of Esthetic Porcelain Restorations", Quintessence of Dental Technology, July/August 1987, pp. 233-242, the most challenging need for reversal of gingival discoloration occurs when a porcelain-fused-to-metal crown is mounted within a dark nonvital tooth having a metal post foundation. Geller et al. explain, at page 239, that the combination of the dark root, opaque crown coping, metal post foundation, and root canal filling material frequently results in the entire tissue area, including attached gingiva and mucosa, acquiring a blue-gray color. Notwithstanding the stated assumption that the metal "post foundation must remain" within the restored tooth, Geller et al. suggest certain crown structures which partially reduce gingival discoloration. A need therefore persists for a product and method for the improved reduction or elimination of gingival discoloration adjacent to dowel-core restored teeth.